The typical construction of a tethered aerial top, commonly referred to as a yo-yo, includes an axle that joins a pair of spaced yo-yo halves and a string that is attached to the axle and can extend radially outwardly through the gap between the spaced yo-yo halves. The other free end of the string is controlled and manipulated by the user to perform various maneuvers and tricks. Many of such maneuvers rely on the ability of the yo-yo to "sleep", that is, to spin while attached to the end of the string without winding the string about the axle and returning to the user. Toward the conclusion of the maneuver, when it is usually desired to cause the yo-yo to return to the user by winding the string about the axle, the user may jiggle the string in a manner that briefly releases the tension on the string. During the brief period that the string may be tension-free and is relatively loose within the gap between the yo-yo halves, the loose string can become frictionally caught between the inwardly facing surfaces of the yo-yo halves. The rotational inertia of the yo-yo halves then causes the yo-yo to climb along the string toward the user, winding the string about the axle as the yo-yo returns to the user. The physics and function of the yo-yo is described in a publication, "The Yo-Yo: A Toy Flywheel" by Wolfgang Buzger, American Scientist, Vol. 72, Par.-Apr. 1984, pp. 137-142.
The width of the gap between the yo-yo halves is critical to proper control of the yo-yo. If the gap is too small, the yo-yo may not sleep, tending, instead, to frictionally grip the string notwithstanding the presence of tension in the string. If the gap is too wide, the inwardly facing surfaces of the yo-yo halves may not be able to engage the string with sufficient friction. Additionally, the width of the gap between the yo-yo halves also affects the precision with which the yo-yo will tend to rotate in a plane. If the gap is too wide, the yo-yo may precess out of a desired plane, resulting in undesirable interference between one of the yo-yo halves and the string, often near the periphery of the yo-yo halves.
Even if the yo-yo gap is set to what might ordinarily be considered a proper gap, with all other components properly balanced and aligned, changing atmospheric conditions can affect the performance of the yo-yo. Most yo-yo strings are formed from cotton that tends to absorb moisture from the air. Consequently, the string may tend to swell in the presence of higher humidity and may tend to shrink in the presence of lower humidity. The humidity also may affect the surface characteristics of the string fibers that, in turn, may affect the frictional interaction between the string and the inner surfaces of the yo-yo halves.
It would be desirable, therefore, to provide a yo-yo in which the gap between the inwardly facing surfaces of the yo-yo could be adjusted in order to maximize the ability of the yo-yo to perform as desired in a particular environment. Adjustment of the gap may, in many cases, compensate for differences in frictional characteristics between the yo-yo string and the inwardly facing, string-engaging surfaces of the yo-yo, whether those characteristics are affected by the composition of the string, the inwardly facing surfaces, atmospheric conditions or any other influence that may affect yo-yo performance. The desirability of providing a yo-yo that is adjustable to compensate for such variations in conditions of use has been recognized and is described in U.S. Pat. No. 5,100,361 (Kuhn). The Kuhn patent describes an arrangement in which the gap between the string-engaging surfaces of the yo-yo can be adjusted. The mechanism described in the Kuhn '361 patent requires that the yo-yo be disassembled in order to provide access to internally adjustable members, that are adjusted by the use of a tool, such as a screw driver. Disassembly to expose an internal, tool-adjustable mechanism presents considerable inconvenience to the user in that play must be interrupted for a considerable period of time. Moreover, even if an adjustment is made, it often may be desirable or necessary to make further fine adjustments to obtain optimum performance. Each such fine adjustment necessarily would require one or more subsequent disassemblies, readjustments and reassemblies of the yo-yo. It would be desirable, therefore, to provide an adjustable-gap yo-yo in which the gap can be adjusted immediately, without requiring disassembly, internal adjustment and reassembly of the yo-yo. It is among the general objects of the invention to provide such a device.